title: Carbon, nitrogen and O(2) fluxes associated with the cyanobacterium Nodularia spumigena in the Baltic Sea.
abstract: Photosynthesis, respiration, N(2) fixation and ammonium release were studied directly in Nodularia spumigena during a bloom in the Baltic Sea using a combination of microsensors, stable isotope tracer experiments combined with nanoscale secondary ion mass spectrometry (nanoSIMS) and fluorometry. Cell-specific net C- and N(2)-fixation rates by N. spumigena were 81.6±6.7 and 11.4±0.9 fmol N per cell per h, respectively. During light, the net C:N fixation ratio was 8.0±0.8. During darkness, carbon fixation was not detectable, but N(2) fixation was 5.4±0.4 fmol N per cell per h. Net photosynthesis varied between 0.34 and 250 nmol O(2) h(-1) in colonies with diameters ranging between 0.13 and 5.0 mm, and it reached the theoretical upper limit set by diffusion of dissolved inorganic carbon to colonies (>1 mm). Dark respiration of the same colonies varied between 0.038 and 87 nmol O(2) h(-1), and it reached the limit set by O(2) diffusion from the surrounding water to colonies (>1 mm). N(2) fixation associated with N. spumigena colonies (>1 mm) comprised on average 18% of the total N(2) fixation in the bulk water. Net NH(4)(+) release in colonies equaled 8-33% of the estimated gross N(2) fixation during photosynthesis. NH(4)(+) concentrations within light-exposed colonies, modeled from measured net NH(4)(+) release rates, were 60-fold higher than that of the bulk. Hence, N. spumigena colonies comprise highly productive microenvironments and an attractive NH(4)(+) microenvironment to be utilized by other (micro)organisms in the Baltic Sea where dissolved inorganic nitrogen is limiting growth.
authors.affiliation: Department of Botany, Stockholm University, Stockholm, Sweden. helle.ploug@ecology.su.se
authors.forename: Helle
authors.initials: H
authors.lastname: Ploug
authors.forename: Birgit
authors.initials: B
authors.lastname: Adam
authors.forename: Niculina
authors.initials: N
authors.lastname: Musat
authors.forename: Tim
authors.initials: T
authors.lastname: Kalvelage
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.forename: Dieter
authors.initials: D
authors.lastname: Wolf-Gladrow
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
mesh_terms: D002244:Carbon / Q000378:metabolism*; D003624:Darkness; D008027:Light; D009584:Nitrogen / Q000378:metabolism*; D046932:Nodularia / Q000254:growth & development / Q000378:metabolism*; D009792:Oceans and Seas; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012623:Seawater / Q000382:microbiology*; D018629:Spectrometry, Mass, Secondary Ion
chemical_list: D000644:Quaternary Ammonium Compounds; D002244:Carbon; D009584:Nitrogen; D010100:Oxygen